Malassezia vespertilionis sp. nov.: a new cold-tolerant species of yeast isolated from bats

Abstract

Malassezia is a genus of medically-important, lipid-dependent yeasts that live on the skin of warm-blooded animals. The 17 described species have been documented primarily on humans and domestic animals, but few studies have examined Malassezia species associated with more diverse host groups such as wildlife. While investigating the skin mycobiota of healthy bats, we isolated a Malassezia sp. that exhibited only up to 92% identity with other known species in the genus for the portion of the DNA sequence of the internal transcribed spacer region that could be confidently aligned. The Malassezia sp. was cultured from the skin of nine species of bats in the subfamily Myotinae; isolates originated from bats sampled in both the eastern and western United States. Physiological features and molecular characterisation at seven additional loci (D1/D2 region of 26S rDNA, 18S rDNA, chitin synthase, second largest subunit of RNA polymerase II, β-tubulin, translation elongation factor EF-1α, and minichromosome maintenance complex component 7) indicated that all of the bat Malassezia isolates likely represented a single species distinct from other named taxa. Of particular note was the ability of the Malassezia sp. to grow over a broad range of temperatures (7-40 °C), with optimal growth occurring at 24 °C. These thermal growth ranges, unique among the described Malassezia, may be an adaptation by the fungus to survive on bats during both the host's hibernation and active seasons. The combination of genetic and physiological differences provided compelling evidence that this lipid-dependent yeast represents a novel species described herein as Malassezia vespertilionis sp. nov. Whole genome sequencing placed the new species as a basal member of the clade containing the species M. furfur, M. japonica, M. obtusa, and M. yamatoensis. The genetic and physiological uniqueness of Malassezia vespertilionis among its closest relatives may make it important in future research to better understand the evolution, life history, and pathogenicity of the Malassezia yeasts.

Keywords: Chiroptera; Malassezia; Myotis; evolution; hibernation; new species; phylogeny.

Fig. 1.

Hibernating bats, such as these Myotis sp., were sampled for this study by swabbing wing skin.

Fig. 2.

Map of the United States, showing the locations of sampling sites from which bats yielded isolates of Malassezia vespertilionis sp. nov. States from which isolates were obtained are labelled (AL = Alabama; CA = California; KY = Kentucky; MO = Missouri; NY = New York; PA = Pennsylvania; WI = Wisconsin).

Fig. 3.

Phylogenetic tree of the genus Malassezia based on concatenated amino acid sequences of 254 conserved orthologues. The tree from the Bayesian analysis is shown, but the tree generated from the maximum likelihood analysis had an identical topology. Posterior probabilities (Bayesian)/bootstrap values (maximum likelihood), respectively, are shown at the nodes. Ustilago maydis was used to root the tree. Clades A, B, C as described by Wu et al. (2015) are illustrated. Based on the analyses, M. vespertilionis sp. nov. is a basal member of clade A.

Fig. 4.

Phylogenetic tree resulting from a Bayesian analysis of concatenated nucleotide sequences from eight loci (ITS, 18S rDNA, D1/D2 region, and portions of the β-tub, TEF1, MCM7, RPB2, CHS2 genes) of 12 Malassezia isolates from bats, all Malassezia species from clade A for which sufficient genetic data was available, and representative members from clades B and C (Wu et al. 2015). Posterior probabilities are presented at each node. All examined isolates from bats formed a well-supported clade, suggesting that they represent a single taxon referred to herein as M. vespertilionis sp. nov.

Fig. 5.

Colony and cell morphology of M. vespertilionis sp. nov. grown on Leeming and Notman Agar at 24 °C. a. Colony size and morphology after 10 d of growth; b. colony size and morphology after 40 d of growth; c. cell morphology of 10-d-old culture. — Scale bars: a, b = 4 mm; c = 5 μm.